[clang] [clang-tools-extra] [clang-tidy] Fix performance-unnecessary-value-param (PR #109145)

[Nicolas van Kempen via cfe-commits]

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nicovank wrote:

This test is passing for me even when I revert `ExprMutationAnalyzer.h` changes. Is it standard library or setup specific?

https://github.com/llvm/llvm-project/pull/109145